Abstract
Purpose :
To evaluate microbial isolation rates following the introduction of a simplified non-invasive method for collecting samples from cases of clinically suspected microbial keratitis over a 2 year period.
Methods :
Data was retrospectively collected by the department of medical microbiology at the Royal Liverpool University Hospital for all patients that had corneal samples taken for suspected microbial keratitis for the period April 2016-April 2018. Samples were collected from ulcers prior to April 2017 by scraping the base of the ulcer with a surgical blade (corneal scrape). From April 2017, samples were collected by placing a 12-mm-diameter polytetrafluoroethylene (PTFE) corneal impression membrane (CIM) over the ulcer. The blade and CIM were transported in brain heart infusion before being plated and sub-cultured in an enrichment medium.
Results :
A total of 1053 cases were included, comprising samples obtained from 448 (42.5%) cases using a corneal scrape and 605 (57.5%) using a CIM. Microorganisms were isolated from 90 (20.1%) cases using a corneal scrape and 396 (65.5%) using a CIM (p<0.001). More than one isolate was identified in 9 (10.0%) and 76 (19.2%) of samples using a corneal scrape and CIM respectively. There was a significant increase in the isolation of pathogens in the CIM group compared to the corneal scrape group (p<0.001); including Staphylococcus aureus (2.0% to 10.1%), Streptococcus pneumoniae (1.3% to 1.7%), Streptococcus pyogenes (0 to 0.3%), Serratia spp. (0.9% to 2.2%), Enterobacteriaceae spp. (0.5% to 1.5%), Moraxella spp. (0.7% to 1.2%) and Pseudomonas spp. (2.0% to 2.6%). Fungi were isolated in 1.1% of the corneal scrape group and 0.5% of the CIM group (p=0.252). There was a significant increase in the isolation of Staphylococcal epidermidis (3.3% to 27.8%) using a CIM (p<0.001).
Conclusions :
The difficulties in isolating the causative microorganism has led to increased empirical treatment of microbial keratitis. The introduction of the simplified CIM sampling method led to a significant increase in the isolation of pathogens from cases of suspected microbial keratitis but also an increase in Staphylococcal epidermidis.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.